1. Field of the Invention
This invention relates to electrical switching apparatus and, more particularly, to circuit breakers employing a trip unit. The invention also relates to circuit breaker trip units.
2. Background Information
Circuit breakers and circuit breaker trip units are well known in the art. See, for example, U.S. Pat. Nos. 5,910,760; and 6,144,271.
Resetting of a circuit breaker (e.g., through the operating handle and operating mechanism thereof) is accomplished in a manner well known in the art and is described and shown, for example, in U.S. Pat. No. 5,910,760.
Industrial circuit breakers often use a modular component called a trip unit. The modular trip unit can be replaced by the customer to alter the electrical properties of the circuit breaker. The trip unit includes a linear plunger, which operates the circuit breaker's operating mechanism and frequently protrudes from the trip unit. See, for example, U.S. Pat. No. 6,144,271, which discloses a circuit breaker frame and internals, and a trip unit.
As disclosed in U.S. Pat. No. 6,144,271, the linear plunger of the trip unit is employed to trip open the associated circuit breaker frame whenever the linear plunger is extended from the trip unit. Actuation of primary and secondary frame latches occurs exclusively by way of the extended and resetable trip unit linear plunger, which is, otherwise, normally contained entirely within the trip unit. The secondary frame latch is in disposition to be struck by an abutment surface of the extended linear plunger. In response to a reset operation, the trip unit is also reset whenever the secondary frame latch drives the extended linear plunger in the opposite direction against its plunger spring and into the trip unit.
The linear travel of the linear plunger often impedes the installation and removal of the trip unit. If the plunger is extended, then awkward assembly and breakage can occur. Also, the linear travel distance of the linear plunger and/or the required travel distance of such linear plunger to cause a trip may be affected by manufacturing tolerances in the trip unit and/or in the circuit breaker frame. Thus, in some circumstances, insufficient travel of the linear plunger may result in no tripping of the circuit breaker.
During a high current interruption, an explosion in the arc chamber of the circuit breaker is the result of rapidly expanding gases. During this explosion, fragments of various circuit breaker components form debris that is expelled throughout the breaker. This debris can become lodged into critical mechanism parts, such as the trip unit linear plunger, causing them to malfunction.
There is a need for an improved circuit breaker employing a trip unit.
There is also a need for an improved circuit breaker trip unit.